History, Synthesis and Properties of Azo Pyridone Dyes

Abstract

Azo dyes are synthetic organic colorants bearing chromophoric azo group. Over 50% of the colorants used belong to the azo compounds. Such a wide range of usage of azo dyes is due to the number of variations in chemical structure and methods of application which are generally not complex. Cotton, paper, silk, leather, and wool can be dyed by azo dyes. Also, there are azo dyes for dying polyamides, polyesters, acrylics, polyolefins, viscose rayon, and cellulose acetate. They can be used for the coloring of paints, varnishes, plastics, printing inks, rubber, foods, drugs, and cosmetics. Azo colorants are also used in diazo printing and color photography. Among azo colorants arylazo pyridone dyes have become important in the last several decades. The high molar extinction coefficient, the medium to high light and wet fastness properties are very favourable. They find application generally as disperse dyes. Disperse dyes are characterized by low aqueous solubility and are applied to hydrophobic fibers from an aqueous system, in which the dye is present in a highly dispersed state. The importance of disperse dyes increased in the 1970s and 1980s due to the use of polyester and nylon as the main synthetic fibers. Also, disperse dyes were used rapidly since 1970. in inks for the heat-transfer printing of polyester as well as for other applications including hot-melt inks, ink-jet inks and color filters for liquid-crystal display panels. Pyrydone azo dyes generally produce yellow shades on fabrics but other shades were also reported. Dye structure affects the intensity of color and fastness properties. Azo pyridone dyes which have OH or NH group in ortho position to azo group show an azohydrazone tautomerism which was investigated in a number of papers. Azo-hydrazone tautomerism was studied in solvents as well as by crystallography. Generally, azo pyridone dyes exist in hydrazone form in the solid state while in solvents azo-hydrazone equilibrium can be found.